1. Field of the Invention
The present invention relates to belt-driven computer tape cartridges and, in particular, to ways of maintaining appropriate tension in the tape in the cartridge.
2. Description of the Related Art
A highly successful elastic belt-driven data cartridge originally was taught in U.S. Pat. No. 3,692,255 (von Behren). In that reference, a tape cartridge has tape wrapped convolutely in opposite directions around hubs and guide pins to guide the tape past the tape drive read/write head. An elastic belt wraps partway around the tape packs on the hubs, as well as around corner rollers and a drive roller. The belt is moved by the drive through frictional rotation of a drive puck by a motor. Provided adequate tension is maintained in the belt, movement of the belt simultaneously will move the tape. Friction at the corner rollers will differentially stretch the belt, which results in tension in the tape so that it can interface properly with the read/write head.
In the past, tension has been maintained in the tape primarily through carefully controlling the amount of friction in the rollers. More recently, use of magnetic hysteresis has been suggested. PCT Published Application No. WO 93/22767 (Alexander et al.).
The problem with either of these techniques is that they depend upon a constant flow of power to overcome either the friction or the magnetic hysteresis and maintain adequate tape tension. The drive must provide that power. No matter how efficient the drive electronics themselves may become, the drive therefore always will consume power to overcome the frictional or magnetic hysteresis losses, producing heat inside the tape cartridge.
Non-belt-driven cartridges theoretically can avoid these frictional losses. For example, U.S. Pat. No. 3,733,529 (Ross et al.), U.S. Pat. No. 4,256,996 (Brooks et al.) and U.S. Pat. No. 4,696,439 (Sukigara et al.) all propose non-belt cartridges driven through their hubs. In each of these designs, a motor/generator is connected to each hub. When the tape is to be driven in one direction, one of these two motor/generators acts as a motor driving the tape, while the other acts as a generator providing drag on the tape. When the tape is moved in the opposite direction, the roles are reversed. In either situation, proper tension in the tape would be maintained by carefully controlling the relative difference in force being applied between the motor and generator.
While such designs theoretically overcome the friction problem, they suffer from very serious drawbacks of their own. First, each of the motors must be relatively large, since it could be the main drive motor depending on the direction in which the tape is moving. Second, the complexity of the control required can be quite high, since the speed of rotation at the hub varies dramatically depending upon the size of the tape pack wound around the hub at any given instant. Such systems therefore are theoretically possible, but expensive.